Second order nonlinear optical chromophores and electro-optic devices therefrom

ABSTRACT

A nonlinear optical chromophore having the formula D-π-A, wherein π is a π bridge including a thiophene ring having oxygen atoms bonded directly to the 3 and 4 positions of the thiophene ring, D is a donor, and A is an acceptor.

RELATED APPLICATIONS

[0001] This application is a continuation-in-part of patent applicationSer. No. 09/932,831 filed Aug. 17, 2001, entitled “Design and Synthesisof Advanced NLO Materials for Electro-Optic Applications,” which isassigned to the same assignee as the present application, which claimsbenefit of Provisional Application No. 60/226,267 filed Aug. 17, 2000,and which is hereby incorporated by reference in its entirety.

[0002] All patents, patent applications, and publications cited withinthis application are incorporated herein by reference to the same extentas if each individual patent, patent application or publication wasspecifically and individually incorporated by reference.

BACKGROUND OF THE INVENTION

[0003] The invention relates generally to the organic chromophores forsecond order nonlinear optical (NLO) applications, compositionsincluding such chromophores, and applications including suchchromophores and compositions.

[0004] The development and uses of NLO chromophores, including polymermatrix development, waveguide fabrication, and optical devicefabrication are well documented. An NLO chromophore (also known as a“push-pull” chromophore) comprises three fundamental building blocksrepresented by the general formula D-π-A, where D is a donor, π is aπ-bridge, and A is an acceptor. In the art, a “π-bridge” is sometimesreferred to as a “π-conjugated bridge,” “π-electron bridge,” “conjugatedπ-electron bridge,” and the like. Examples of such bridges aredescribed, for example, in U.S. Pat. Nos. 5,670,091, 5,679,763,6,067,186, and 6,090,332. A “π-bridge” allows charge transfer from adonor to an acceptor in a chromophore. Exemplary acceptors are shown inFIG. 1, where, independently at each occurrence, R¹ is hydrogen, ahalogen except when bonded to a carbon alpha to or directly to anitrogen, oxygen, or sulfur atom, or an alkyl, aryl, heteroalkyl, orheteroaryl group; Y is O, S or Se; and q is 0 or 1. Exemplary donors areshown in FIG. 2, where, independently at each occurrence, R¹ ishydrogen, a halogen except when bonded to a carbon alpha to or directlyto a nitrogen, oxygen, or sulfur atom, or an alkyl, aryl, heteroalkyl,or heteroaryl group; R² is hydrogen or an alkyl, aryl, heteroalkyl, orheteroaryl group; Y is O, S or Se; m is 2, 3 or 4; p is 0, 1 or 2; and qis 0 or 1. Herein, a heteroalkyl group includes, but is not limited to,functional groups, halogen substituted alkyl groups, perhalogenatedalkyl groups, and dendrons. What is meant by a functional group ingenerally understood in the art of organic chemistry, for example seeAppendix B in Jerry March, “Advanced Organic Chemistry” 4^(th) Edition,John Wiley and Sons, New York, pp 1269-1300. A “dendron” is asubstituent that has regularly repeating subunits. A dendron may befurther comprised of one or more heteroaryl group. A “dendrimer” is amacromolecular structure that contains a “core” surrounded by one ormore dendrons. Often in the art, the terms dendron and dendrimer areused interchangeably. Dendrons and dendrimers are illustrated anddiscussed in Bosman et al., Chem. Rev. 1999, 99, 1665 and U.S. Pat. No.5,041,516.

[0005] The particular D-π-A arrangement affects the ability of themolecule to achieve large second order NLO effects. Thus, the firstmolecular electronic hyperpolarizability (β, sometimes given as μβ,where μ is the dipole moment of the chromophore), which is a measure ofthis ability, can be tuned and optimized by changing the electronicproperties of any one of D, π, or A, see Gorman and Marder Proc. Natl.Acad. Sci, USA 1993, 90, 11297. Molecular NLO effects, in turn, can betranslated into bulk EO activity in a material by aligning molecules inone direction by applying an electric field.

SUMMARY OF THE INVENTION

[0006] In one aspect, a nonlinear optical chromophore has the formulaD-π-A where π is a π bridge including a thiophene ring having oxygenatoms bonded directly to the 3 and 4 positions of the thiophene ring, Dis a donor, and A is an acceptor. The oxygens bonded directly to the 3and 4 ring positions of the of the thiophene ring may be furtherindependently substituted with an alkyl group comprising 1 to about 20carbons, a heteroalkyl group comprising 1 to about 20 carbons, an arylgroup comprising 1 to about 20 carbons, or a heteroaryl group comprising1 to about 20 carbons.

[0007] In a second aspect, a nonlinear optical chromophore has theformula:

[0008] wherein, independently at each occurrence: π¹ is absent or aπ-bridge; π² is absent or a π-bridge; D is an donor; A is an acceptor; Xis O or S; and R is an alkyl group comprising 1 to about 20 carbons, aheteroalkyl group comprising 1 to about 20 carbons, an aryl groupcomprising 1 to about 20 carbons, or a heteroaryl group comprising 1 toabout 20 carbons..These chromophores may be combined with a polymermatrix to form second order nonlinear optical compositions useful in avariety of applications, including electro-optic devices such as opticalmodulators, optical switches, and optical directional couplers. Forexample, the chromophore and polymer matrix may contain crosslinkablefunctional groups, and may be combined to form a guest-host composite,in which the chromophore is the guest and the polymer matrix is thehost. An electric field is then applied to the composite to induceelectro-optic activity, after or during which the composite iscrosslinked to covalently bond the chromophore to the polymer matrix.Other features and advantages of the invention will be apparent from thefollowing description of preferred embodiments thereof, and from theclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 illustrates exemplary acceptors that can be used in someembodiments.

[0010]FIG. 2 illustrates exemplary donors that can be used in someembodiments.

[0011] FIGS. 3-6 outline syntheses of various nonlinear opticalchromophores.

[0012]FIG. 7 outlines a synthesis of a crosslinkable polymer used insome embodiments.

DETAILED DESCRIPTION

[0013] The second order nonlinear optical chromophores have the chemicalstructures and formulas described above in the Summary of the Invention.Examples of donors (D) that may be used include structures chosen fromthe group consisting of

[0014] Examples of acceptors (A) that may be used include structuresselected from the group consisting of

[0015] wherein independently at each occurrence: R¹ is hydrogen, ahalogen except when bonded to a carbon alpha to or directly to anitrogen, oxygen, or sulfur atom, or an alkyl, aryl, heteroalkyl, orheteroaryl group; R² is hydrogen or an alkyl, aryl, heteroalkyl, orheteroaryl group; Y is O, S or Se; m is 2, 3 or 4; p is 0, 1 or 2; and qis 0 or 1. Preferably, the donor is chosen from the group consisting of

[0016] wherein independently at each occurrence: R¹ is hydrogen, ahalogen except when bonded to a carbon alpha to or directly to anitrogen, oxygen, or sulfur atom, or an alkyl, aryl, heteroalkyl, orheteroaryl group; and R² is hydrogen or an alkyl, aryl, heteroalkyl, orheteroaryl group.

[0017] The chromophores may be combined with a polymer matrix to formcompositions useful in a variety of electro-optical applications. Suchcompositions may be prepared according to a number of known techniques,including those described in U.S. Pat. No. 5,776,374; 5,714,304;5,223,356; 5,433,895; 6,294,573; 6,126,867; 5,811,507; 5,635,576;5,520,968; 5,359,008; 5,266,365; 5,207,952; and 6,228,977 and Chem.Mater. 2000, 12, 1187; J. Am Chem. Soc. 2001, 123, 986; Macromolecules1992, 25, 4032; Chem. Mater. 1999, 11, 2218; and Chem. Mater. 1998, 10,146. In one embodiment, the chromophore is a guest in the crosslinkedpolymer matrix host. In another embodiment, the chromophore iscovalently incorporated into a crosslinked polymer matrix, thechromophore being at first a guest in a crosslinkable polymer matrixhost.

[0018] Another embodiment is a process comprising: 1) providing a guestchromophore in a polymer host, wherein both the guest chromophore andpolymer host contain fluorinated crosslinkable groups; 2) applying anelectric field to the composite to induce electro-optic activity; and 3)crosslinking the composite, whereby the chromophore guest is covalentlyincorporated into the polymer host to provide a crosslinked nonlinearoptical material. This method has advantages over other conventionalprocesses, such as: 1) the chromophore guest and polymer host arecompatible due to both having fluorinated crosslinkable groups; 2) thenonlinear optical material produced will have lower loss at 1550 nmsince the crosslinking groups are fluorinated; 3) the chromophore hosthas more degrees of freedom to align with the poling field since it isnot covalently incorporated into the polymer host before the polingfiled is applied; and 4) the molecular weight and composition of thepolymer are precisely known, which will allow control of criticalparameters like film thickness, T_(g), and solubility.

[0019] The nonlinear optical compositions may be used to fabricateoptical devices, optical switches, modulators, waveguides, or otherelectro-optical devices that can be used in communication systems usingmethods known in the art. For example, in optical communication systems,devices fabricated including compositions described above may beincorporated into routers for optical communication systems, waveguidesfor optical communication systems, or for optical switching or computingapplications. Because polymers are generally less demanding thancurrently used materials, devices including compositions described abovemay be more highly integrated.

[0020] Specific examples of components of optical communication systemsthat may be fabricated in whole or in part from the nonlinear opticalcompositions described above include, without limitation, straightwaveguides, bends, single-mode splitters, couplers (includingdirectional couplers, MMI couplers, star couplers), routers, filters(including wavelength filters), switches, modulators (optical andelectro-optical, e.g., birefringent modulator, the Mach-Zenderinterferometer, and directional and evanescent coupler), arrays(including long, high-density waveguide arrays), optical interconnects,optochips, single-mode DWDM components, and gratings.

[0021] Waveguides made with nonlinear optical compositions describedabove may be used in telecommunication, data communication, signalprocessing, information processing, and radar system devices and thusmay be used in communication methods relying, at least in part, on theoptical transmission of information. Specific applications in which theabove-described nonlinear optical compositions can be incorporatedinclude:

[0022] (1) an electro-optic device that is an interferometric opticalmodulator or switch, comprising: 1) an input waveguide; 2) an outputwaveguide; 3) a first leg having a first end and a second end, the firstleg being coupled to the input waveguide at the first end and to theoutput waveguide at the second end; and 4) and a second leg having afirst end and a second end, the second leg being coupled to the inputwaveguide at the first end and to the output waveguide at the secondend, wherein at least one waveguide includes a nonlinear opticalcomposition described above.

[0023] (2) an optical modulator or switch, comprising: 1) an input; 2)an output; 3) a first waveguide extending between the input and output;and 4) a second waveguide aligned to the first waveguide and positionedfor evanescent coupling to the first waveguide; wherein at least onewaveguide includes a nonlinear optical composition described above.

[0024] (3) an optical router that includes at least one opticalmodulator, optical switch, or optical directional coupler comprising anonlinear optical composition described above.

[0025] Additional applications include a communications system includingat least one electro-optic device comprising a nonlinear opticalcomposition described above, a method of data transmission includingtransmitting light through a nonlinear optical composition describedabove, a method of telecommunication including transmitting lightthrough a nonlinear optical composition described above, a method oftransmitting light including directing light through or via a nonlinearoptical composition described above, and a method of routing lightthrough an optical system comprising transmitting light through or via anonlinear optical composition described above.

[0026] Additionally, the nonlinear optical compositions described hereinmay be applied to devices or methods that control the phase of lightwaves passing through the material. In some applications, electricalfields are applied across a set of waveguides through which the lightwaves travel. Controlling the electrical fields allows the relativephases of the light waves to be controlled. Such approaches areparticularly useful in applications known in the art such asphased-array radar or phase matching of light waves passing throughalternative waveguides, for example see, U.S. Pat. Nos. 5,353,033;5,051,754; 4,258,386; and 4,028,702. Thus, another embodiment is aphased-array radar comprising a nonlinear optical composition embodimentdescribed above.

[0027] The following examples are illustrative and are not intended as alimitation thereof.

EXAMPLES Example 1

[0028] Referring to FIG. 3, Compound 1, which was prepared as in Syn.Comm. 1996, 26, 2213, (187.8 g, 0.824 mol), dry DMF (127.4 mL, 1.647mol) and dry dichloromethane (2000 mL) were mixed in a 3-neck flask andcooled to 0° C. POCl₃ (201.6 g, 1.318 mol) was added. The mixture washeated to reflux for 3 h. Then it was poured into 1 M NaOAc solution. Itwas extracted with CH₂Cl₂, washed with water and dried over MgSO₄. Afterremoving the solvent, it was purified by flash column with ethylacetate/hexane (1:2.5) to give 200 g (95%) of Compound 2.

[0029] Zinc (61.5 g, 0.941 mol) and dry THF (950 mL) were placed in a3-neck flask and cooled to 0° C. TiCl₄ (51.5 mL, 0.469 mol) was addedslowly. The mixture was then heated to reflux for half hour. It was thencooled to 0° C. A solution of compound 2 (60 g, 0.234 mol) and pyridine(49.5 mL, 0.605 mol) in THF (200 mL) was added slowly. The mixture washeated to reflux for 2 h. After cooling to room temperature, ice andCH₂Cl₂ were added. The resulting mixture was filtered through zelite,washed with HCl solution, water and dried over MgSO₄. After removing thesolvent, the crude solid was purified by recrystallization from methanolto give 42.4 g (75%) of Compound 3.

[0030] Compound 3 (75 g, 0.156 mol) and ether (1400 mL) were placed in aflask and cooled to 0° C. BuLi (2.5 M) (156 mL, 0.39 mol) was addedslowly and stirred for 15 min. DMF (57 mL, 0.733 mol) was then added,after which the mixture was warmed to room temperautre and stirred.NH₄Cl solution was added and the solvent was partially removed underreduced pressure. It was then extracted with CH₂Cl₂, washed with water,and dried over MgSO₄. After removing the solvent, the crude product waspurified by recrystallization from methanol to give 76 g (91%) ofCompound 4.

[0031] Compound 5 (2.74 g, 5.44 mmol) and THF (200 mL) were mixed andstirred. At −40° C., BuLi (2.5 M) (2.4 mL, 5.98 mmol) was added and thenstirred at room temperature for 30 min. The resulting solution was addedslowly to a solution of Compound 4 (2.65 g, 4.94 mmol) in 100 mL THFwith stirring. The solution was stirred at room temperature for 8 h,after which the solvent was removed at reduced pressure. The remainingcrude material was purified by column chromatography withhexane/CH₂Cl₂/ethyl acetate mixture to give 2.65 g (76%) of Compound 6(which may have a slight impurity of di-reacted product).

[0032] Compound 6 (2.65 g, 3.9 mmol), Compound 7 (1.55 g, 7.8 mmol),CHCl₃ (2 mL), and piperidine (2 drops) were mixed and refluxed for 3 h.The reaction was monitored with thin layer chromatography until the bulkcolor changed to dark blue/green. The product was purified by flashcolumn and regular column chromatography with CH₂Cl₂/ethylacetate/hexane mixture to give 1.5 g (45%) of Compound 8.

[0033] An electro-optic polymer thin film including chromophore Compound8 was prepared by: 1) obtaining a solution of Compound 8 and poly[biphenyl A carbonate-co-4,4′-(3,3,5-trimethylcyclohexylidene)-diphenolcarbonate] from Aldrich (27% by weight loading of Compound 8 withrespect to the polycarbonate) in dibromomethane (6.67% by weight loadingof the dibromomethane with respect to Compound 8 and the polycarbonate);2) spin depositing the solution at 500 rpm for 5 sec and 1500 rpm for 30sec on a 2″ diameter indium tin oxide (ITO) substrate; 3) sputtering agold electrode on the polymer thin film; and 4) poling at 124° C. for5-10 min in silicon oil with a poling voltage of 100-150 V/μm.

Example 2

[0034] Referring to FIGS. 4-6, Compound 9 (82 g, 0.107 mol) and THF(2500 mL) were mixed and stirred. At −40° C., BuLi (2.5 M) (47.4 mL,0.118 mol) was added and then stirred at room temperature for 30 min.The resulting solution was added slowly to a solution of Compound 4 (50g, 0.093 mol) dissolved in 1500 mL THF. The resulting solution was thenstirred at room temperature for 8 h. The solvent was removed at reducedpressure. The remaining crude material was purified by columnchromatography with hexane/CH₂Cl₂/ethyl acetate mixture to give 61.3 g(70%) of Compound 10.

[0035] Compound 10 (61 g, 0.065 mol), Compound 7 (26 g, 0.129 mol),CHCl₃ (20 mL) and piperidine (10 drops) were mixed and refluxed for 3 h.The reaction was monitored with thin layer chromatography until the bulkcolor changed to dark blue/green. The product was purified by flashcolumn and regular column chromatography with CH₂Cl₂/ethylacetate/hexane mixture to give 36 g (49%) of Compound 11.

[0036] Compound 11 was dissolved in 750 mL THF. HCl solution (1 N, 250mL) was added and the resulting solution was stirred for 8 h. Afterchecking the reaction with thin layer chromatography, NaHCO₃ solutionwas added. The resulting solution was then extracted with CH₂Cl₂, washedwith water, and dried over MgSO₄. After removing the solvent underreduced pressure, the remaining material was purified by flash columnchromatography with CH₂Cl₂/ethyl acetate mixture to give 17.8 g (63%) ofCompound 12.

[0037] Compound 13, which can be prepared as in U.S. Pat. No. 5,198,513or by carbonylation of the lithium salt of Compound 15 (FIG. 7) followedby reaction with thionyl chloride, (23.5 g, 0.099 mol) was dissolved in50 mL CH₂Cl₂ and cooled to 0° C. Compound 12 (17.8 g, 0.0199 mol) andpyridine (9.6 mL, 0.119 mol) were dissolved in 200 mL CH₂Cl₂ and addedslowly to the solution of Compound 13. The resulting solution wasstirred at room temperature for 8 h. The mixture was then extracted withCH₂Cl₂, washed with water, and dried over MgSO₄. After removing thesolvent under reduced pressure, the remaining material was purified byflash column chromatography with CH₂Cl₂/ethyl acetate mixture to give 21g (83%) of Compound 14.

[0038] Referring to FIG. 7, a three-neck 500 ml flask equipped with athermometer, a magnetic stirrer bar, and an addition funnel was chargedwith 25.3 g (0.1 mol) of Compound 15, which can be prepared as inMacromolecules 1996, 29(3), 852-860). The flask was purged with nitrogenbefore introducing 200 mL of dry ether and then was cooled in dryice-acetone bath. 76 mL of 1.7 M t-BuLi in pentane was dropped intoflask from addition funnel below −65° C. After completion of thisaddition, the reaction was kept in the above bath for 1 hour. 19.4 g of2,3,4,5,6-pentafluorostyrene was then added and allowed to react for 1 hbefore removing the cooling bath and letting the temperature reach 0° C.At this moment, dilute HCl aqueous solution was poured into the flask toquench the reaction until the aqueous layer became acidic. The organiclayer was separated, dried over MgSO₄, evaporated, and purified on asilica gel column with hexanes to give Compound 16 as a white solid(10.08 g, 29%).

[0039] A mixture of Compound 16, (1.7411 g, 5.0 mmol), THF (5 mL), and2,2′-azoisobutyronitrile (AIBN) in a 25 mL flask equipped with acondenser was kept under nitrogen atmosphere at 76° C. for 5 hours and60° C. overnight. The reaction was allowed to cool and the polymer wascollected after precipitation by the addition of hexanes and filtrationto give 1.2 g of Polymer 17 as a white powder.

[0040] A crosslinked electro-optic polymer thin film including Compound14 in Polymer 17 was prepared by: 1) preparing a solution of Compound 14and Polymer 17 (15% by weight loading of Compound 14 with respect toPolymer 17) in cyclopentanone (30% by weight loading of cyclopentanonewith respect to Compound 14 and Polymer 17); 2) spin depositing thesolution at 500 rpm for 5 sec and 1300 rpm for 30 sec on a 2″ ITOsubstrate; 3) corona poling the system at 180° C. and 4.5 kV for 10 min,5.5 kV for 5 min, 6.5 kV for 5 min, and 7.5 kV for 5 min; and 4)allowing the crosslinked film to cool to room temperature under the 7.5kV field.

[0041] Other embodiments are within the following claims.

What is claimed is:
 1. A nonlinear optical chromophore having the formula D-π-A, wherein π is a π bridge including a thiophene ring having oxygen atoms bonded directly to the 3 and 4 positions of the thiophene ring, D is a donor, and A is an acceptor.
 2. The chromophore of claim 1, wherein the oxygen atoms are independently substituted with an alkyl, heteroalkyl, aryl, or heteroaryl group.
 3. A nonlinear optical chromophore having the formula:

wherein, independently at each occurrence: π¹ is absent or a π-bridge; π² is absent or a π-bridge; D is an donor; A is an acceptor; X is O or S; and R is an alkyl, aryl, heteroalkyl, or heteroaryl group.
 4. The chromophore of claim 1, 2, or 3 wherein the donor is selected from the group consisting of:

and the acceptor is selected from the group consisting of

wherein independently at each occurrence: R¹ is hydrogen, a halogen except when bonded to a carbon alpha to or directly to a nitrogen, oxygen, or sulfur atom, or an alkyl, aryl, heteroalkyl, or heteroaryl group; R² is hydrogen or an alkyl, aryl, heteroalkyl, or heteroaryl group; Y is O, S or Se; m is 2, 3 or 4; p is 0, 1 or 2; and q is 0 or
 1. 5. The chromophore of claim 4, wherein the donor is selected from the group consisting of

wherein, independently at each occurrence: R¹ is hydrogen, a halogen except when bonded to a carbon alpha to or directly to a nitrogen, oxygen, or sulfur atom, or an alkyl, aryl, heteroalkyl, or heteroaryl group; and R² is hydrogen or an alkyl, aryl, heteroalkyl, or heteroaryl group.
 6. The chromophore of claim 3, wherein each X is oxygen and each R group is an alkyl group.
 7. A second order nonlinear optical composition comprising a polymer matrix and a chromophore according to claim 1, 2, or
 3. 8. The composition of claim 7, wherein the chromophore is covalently incorporated into the polymer matrix.
 9. The composition of claim 7, wherein the polymer matrix is crosslinked.
 10. The composition of claim 8, wherein the polymer matrix is crosslinked.
 11. An electro-optic device, comprising the second order nonlinear optical composition of claim
 7. 12. The electro-optic device of claim 11, wherein the electro-optic device is selected from the group consisting of an optical modulator, an optical switch, and an optical directional coupler.
 13. The electro-optic device of claim 11, comprising: 1) an input waveguide; 2) an output waveguide; 3) a first leg having a first end and a second end, the first leg being coupled to the input waveguide at the first end and to the output waveguide at the second end; and 4) and a second leg having a first end and a second end, the second leg being coupled to the input waveguide at the first end and to the output waveguide at the second end.
 14. The electro-optic device of claim 11, comprising: 1) an input; 2) an output; 3) a first waveguide extending between the input and output; and 4) a second waveguide aligned to the first waveguide and positioned for evanescent coupling to the first waveguide.
 15. An optical router including the electro-optic device of claim
 11. 16. A communications system including at least one electro-optic device of claim
 11. 17. A method of data transmission comprising transmitting light through the composition of claim
 7. 18. A method of telecommunication comprising transmitting light through the composition of claim
 7. 19. A method of transmitting light comprising directing light through or via the composition of claim
 7. 20. A method of routing light through an optical system comprising transmitting light through or via the composition of claim
 7. 21. A phased array radar system comprising the composition of claim
 7. 